Not Applicable
Not Applicable
1. Field of the Invention
This invention relates generally to conditioning the forced air of downdraft types of paint booths that are used in the automotive repair industry. Particularly, it relates to an improvement in management, conditioning and control of the air flow in order to improve and maintain comfortable working and breathing environment, thereby ensuring a better level of health and safety for painting personnel. Specific to the invention is the concept of emulating operation of a large-capacity cooling system with multiple smaller air conditioners.
2. Discussion of Relevant Art
Those associated with modern automotive body repair facilities are acquainted with Occupational Health and Safety Act (OSHA) requirements as they pertain to the work environment that must be maintained in the facilities used for painting. Foremost among the health and safety standards are those that deal with the handling, use and disposal of noxious paint and solvent fumes. To this end, there is extensive use of air moving and air conditioning equipment, including that for ventilation as well as humidifying, and heating or cooling the air for paint curing. Most paint facilities consist in rooms or booths that are spacious enough to enclose the object to be painted, while affording adequate space for one or two persons, with spray equipment, to move comfortably about the particular facility. In high production facilities, wherein the two cyclesxe2x80x94painting and curingxe2x80x94are run throughout the workday, a cool down problem may occur in most locations in the temperate weather zone. This problem occurs primarily because the curing heat required in the facility (hereafter, xe2x80x9cboothxe2x80x9d) is not ameliorated rapidly enough to allow comfortable reentry by the painter(s). Ambient humidity and temperature, at the beginning of the day, are readily handled by most systems, during the incipient operation, but not as the day progresses. Consequently, personnel are often subjected to arduous working conditions which, on days of high temperature and/or humidity, create an issue of health and safety.
In this discussion of relevant art, I want to first describe the type of facility that I originally purchased and have subjected to the hereinafter discussed improvements. My booth is a product of S.A.I.M.A.; Arezzo, Italy, imported by Pippa Industries, Paterson, N.J. The equipment provision for this drive-in enclosure is, in the sequence of principal air flow: intake; air ducting; adjacent damper (not in the direct intake air stream); air mover; furnace; a ducting subsystem that communicates with both the intake stream (via an adjacent damper) and the booth ceiling (via a plenum); ceiling filtration; booth enclosure; floor filtration; and an exhaust duct, leading to ambient atmosphere. [There was no air conditioner provided in the original booth.]
During the xe2x80x9cbakingxe2x80x9d or curing cycle, the personnel are evacuated and, by use of the control system, the furnace is activated for high(er) heat and the damper is positioned to partially re-circulate the heated air into the intake stream. Re-circulation of the heated air induces a rapid heat rise to acquire a metal temperature (of the vehicle) of 140xc2x0 F. (60xc2x0 C.). Immediately after the curing cycle, the air flow is restored and the damper is repositioned to reinitiate the xe2x80x9cpaintxe2x80x9d cycle. In the original, unimproved system, booth cool down, from about 100xc2x0 F. to about 75xc2x0, took an average of nine minutes or more, depending on outside temperature. During the paint spraying operation, a single air conditioner (xe2x80x9cA/Cxe2x80x9d), that I retrofitted to the original booth, cycled an average of every four minutes, with temperature varying as much as 18xc2x0 F. On the second painting cycle of the day, recovery to tolerable conditions for personnel was acceptable (about eight minutes). However, as the day progressed, and both ambient outside and equipment temperatures rose, the recovery time became protracted (to as long as, or longer than 20 minutes). Often, on humid days over 85xc2x0 F., the air conditioning unit failed to recover sufficiently, requiring a shut down in operations and posing, for me, the most significant deficiency in my operation.
I cannot say how other systems, made by other manufacturers, perform; however, a relevant art search has shown the equipment and techniques employed by them and prompted me to disclose my recent improvements.
The systems of interest are downdraft types that essentially provide air through the overhead structure and exhaust through the floor on which the work piece resides. U.S. Pat. No. 5,213,259, issued for Paint Booth Humidity and Temperature Control System, is directed toward a humidity control system that uses a water spray nozzle to rapidly alter the humidity and, consequently, the temperature of air taken into a paint booth through its ceiling. The air is drawn across the work piece, front to rear, and exhausted through the same ceiling. Being of a substantially different draft type than required by my operation, this system is noted only in that no provisions appear to have been made for balancing personnel comfort against high productivity requirements. In U.S. Pat. No. 5,127,574, issued for Spray Booth for Applying Coatings to a Substrate and Control Device Therefore (sic), shows a down draft type paint system that uses an open booth, similar to a laboratory hood, save for the downward flow. It displays only a spraying apparatus and, absent a heat curing setup, is not fully within the purview of my invention. U.S. Pat. No. 3,979,535, issued for Process for the Spray Application of Aqueous Paints by Controlling the temperature of the Air in the Paint Spray Zone is relevant in that it discloses a system for modifying spray air during the painting cycle. This technique is inapplicable to the treatment of booth air, in general; it is cited because it discusses the relationship that environmental humidity bears to ambient temperature and the coating (painting) process.
Two patents having similar tangential relevance, in that working persons are not of particular concern nor employed, are U.S. Pat. Nos. 4,367,787 and 4,616,594, issued for Air Conditioning Apparatus and Method for Paint Spray Booths and Painting Booth, respectively. The first of these consists in a single air conditioner system that uses a multiply-sectioned heat exchanger and partitioned air flow treatment to effectively recover and conserve energy while providing a customized mix of conditioned and unconditioned (bypassed) air to a paint booth (not disclosed). The second employs a single air conditioner, but is concerned only with providing temperature and humidity controlled air to an unmanned or robotic system, and within a very small zone. Of particular interest to me is its similarity to my present system, but for lack of a human element and the sparseness of the area of work.
A most notable deficiency with single, large-capacity air conditioners is that, with the requirement to maintain tolerable work conditions (by keeping the temperature environment within a few degrees), the cooling system must turn on/off frequently. This characteristic is deleterious to all machinery, irrespective of size.
In the aggregate, U.S. Pat. Nos. 4,616,594, 5,127,574 and 5,213,259 show many of the aspects of the original paint booth facility that I have improved for human comfort and safety, e.g., downdraft type, ceiling and floor filtration, at most a single air conditioner or partial re-circulation. All are hereinafter incorporated by reference.
Terms used herein shall have their standard meanings which are taken ordinarily from the American Heritage Dictionary of the English Language 2000. In the case of a word or term to which is ascribed a particular meaning of art, the word will be used in context, defined, and setoff by quotation marks (xe2x80x9c)
I have succeeded in improving the health and safety conditions of personnel that work in my paint spraying facilities, without suffering any measurable loss of product or profit, while still avoiding the high on/off cycling rate of the principal cooling facility. Where I have invested to purchase equipment, I have gained by decreasing inoperative situations or periods (xe2x80x9cdown timexe2x80x9d), thus increasing production and concurrently ensuring a greater degree of comfort for my workers.
The most notable factor in modem, manned spray booths, that leads to excessive down times, is the variation in booth circulating air temperature, exacerbated by multiple, prior baking/curing operations. Recovery times of 20-30 minutes, for booth cool down from 100xc2x0 F. to 75xc2x0, combined with booth air temperature variation of up to 18 degrees, from the desired xe2x80x9cbasexe2x80x9d temperature of 70xc2x0 F., are common. The air conditioner (xe2x80x9cA/Cxe2x80x9d) will run (xe2x80x9ccyclexe2x80x9d) every 3-5 minutes and, quite often, shut down completely due to overheating; its recovery time being dependent on outside ambient air temperature and the difference (xe2x80x9cxcex94Txe2x80x9d or xe2x80x9csetoffxe2x80x9d) between the set maximum/minimum temperatures at which the single A/C turns on/off.
In order to cure the above-mentioned deficiency, I have devised a method of utilizing more than one A/C (two are suitable to my particular needs), that are each responsive to an independent and discretely placed temperature sensor, and have regulated the operation of this multiplicity of A/Cs to ensure that at least one will run (i.e., continual cooling rather than dependently cycling over a setoff range, ibid.) during the paint spraying cycle, when outside temperatures exceed my desired base temperature (ibid.). To achieve this, I have placed my dual A/C temperature sensors in a stylized arrangement that allows the emulation of a (preset) setoff, as used in the solitary A/C plant. In essence, I acquire a xcex94T by locating, with ordinary thermometers, physically separated positions in the booth plenum wherein the desired temperature difference of xc2x13xc2x0 may be observed. The first sensor placement is close to the point of air introduction to the plenum; the second is toward the most distant (or xe2x80x9cdistalxe2x80x9d) part of the plenum, sufficient to acquire a xcex94T of about six degrees (xc2x13xc2x0). Each A/C is configured to operate at the preset temperature, having an inherent setoff of xc2x10.5xc2x0, the first responding to its sensor at a nominal 67xc2x0 F. (turn on/off at 67.5xc2x0/66.5xc2x0) and the second, a nominal 73xc2x0 F. (turn on/off at 73.5xc2x0/72.5xc2x0). Thus, between the respective low and high points, the desired base of 70xc2x0 F.xc2x13xc2x0 is attained by the multiple air conditioner system, emulating a single one; and, so long as ambient temperatures exceed 70xc2x0, at least one A/C is compelled to run by the controller, monitoring the sequencing of the A/Cs. Where cost is not necessarily an object, more than one controller may be used to set individual temperature ranges for the sensors, thus acquiring smaller or greater variations.
All A/Cs shut down at commencement of the baking/curing cycle, when personnel have exited the booth and re-circulation of booth air is initiated. The baking cycle normally lasts up to 45-50 minutes, during which the air temperature rises to 180xc2x0 F., heating both the work piece and the booth interior to at least 140xc2x0 F.
When the instant improvements to the system are properly installed/operated, the results are remarkable: single A/C cycling time or outside air temperature is no longer a concern; booth circulating air temperature varies by plus or minus three degrees (xc2x13xc2x0); and, operational recovery times are reduced to an average of four minutes, throughout the work day.